complacency (n.)

mid-15c., "pleasure, gratification," especially "self-satisfaction, delight in one's condition" (c. 1500), from Medieval Latin complacentia "satisfaction, pleasure," from Latin complacentem (nominative complacens), present participle of complacere "to be very pleasing," from com-, here perhaps an intensive prefix (see com-), + placere "to please" (see please (v.)). The sense of "disposition to please" (1620s) now goes with complaisance.